This invention relates generally to electrical circuit breakers and, more specifically, to electrical circuit breakers including electronic components.
Electrical circuit breakers interrupt the current flow in electrical circuits when the circuit breaker detects a fault in the electrical circuit. Most circuit breakers rely on the heat induced in a bimetal conductor by excess current to deform the bimetal conductor, which induces a mechanical action that physically breaks the circuit. These circuit breakers are often referred to as xe2x80x9cthermalxe2x80x9d circuit breakers. Recent improvements to circuit breakers utilize electronics to detect circuit faults that a purely thermal circuit breaker may not respond to, in part because the faults do not necessarily result in a sustained over-current situation. Examples of these circuit faults include arc faults and ground faults. If the electronics detect a fault condition, the electronics generate a signal that xe2x80x9ctripsxe2x80x9d the circuit breaker, generally by activating a solenoid that induces a mechanical action to physically break the circuit. Not only do the electronics provide the means to detect these fault conditions, they permit the circuit breaker to respond to these conditions long before an over-current situation developsxe2x80x94if such an over-current situation develops at all.
No longer simple electromechanical devices, the electronics in present day circuit breakers must be powered. A challenge is that the electronics should be powered in such a way that there is not a conductive path bridging the break in the circuit provided by the circuit breaker when the circuit breaker is in the off position or has been tripped. Presumably, this means powering the electronics from one or the other side of the physical separation provided by the circuit breaker. Generally, the side connected to the power source is referred to as the xe2x80x9clinexe2x80x9d side, while the other side is referred to as the xe2x80x9cloadxe2x80x9d side. When the circuit breaker is turned xe2x80x9conxe2x80x9d or xe2x80x9creset,xe2x80x9d the line side is electrically connected to the load side, forming the circuit that the circuit breaker protects. When the circuit is complete or xe2x80x9cclosedxe2x80x9d (the circuit breaker is on), whether the electronics are powered from the line side or the load side may make little difference. However, when the circuit is incomplete or xe2x80x9copenxe2x80x9d (the circuit breaker is off or tripped), the side from which the electronics are powered determines whether the electronics actually receive power while the circuit breaker is in the open condition. This has practical consequences, for instance, if the electronics are powered from the load side, there is a latency in protection by the electronics from the time that the circuit breaker is turned on until the electronics xe2x80x9cpower upxe2x80x9d to their useful state. This is particularly important in a xe2x80x9cresetxe2x80x9d situation, where the circuit breaker may have previously detected a fault that caused the circuit breaker to trip. Insuring that the electronics are powered from the line side (or the load side, as the application may dictate), is often a design and implementation requirement for a circuit breaker.
In the airplane industry, circuit breaker mounting locations are keyed to accept thermal circuit breakers in one specific orientation. Once the circuit breakers have been mounted in a panel, one electrical terminal is bolted to a solid line bus bar while the other terminal receives a terminal lug crimped onto a load wire. Prior to the introduction of electronic components into circuit breakers, the electromechanical basis of a thermal circuit breaker made the orientation of the line and load connections with respect to the terminals of the circuit breaker irrelevant. This led panel designers to route line buses and load wires in the most convenient configuration possible, many times interchanging the orientation of the line and load terminals with respect to the keyed mounting locations of the circuit breakers.
Densely packed circuit breaker panels, keyed mounting locations, solid line bus bars, and tightly secured wire bundles make retrofitting these panels to accept circuit breakers that require a specific orientation a difficult and expensive proposition. Instead of reconfiguring a circuit breaker panel, one could provide a different circuit breaker for each orientation and current rating, e.g., one part for line bus configuration xe2x80x9cAxe2x80x9d and another separate part for line bus configuration xe2x80x9cBxe2x80x9d. This at least doubles the part number quantities, causing additional expense for manufacturing, ordering and inventory, among other things. More importantly, the improper installation of circuit breakers can defeat the added safety afforded by the fault detection circuitry in the improved circuit breakers.
There exists a need for a reversible circuit breaker that includes fault detection electronics. The reversible circuit breaker preferably should include an automatic voltage source selector to set a power source path to its electronics package. Preferably, the automatic voltage source selector automatically detects a power source path from among a plurality of power source paths and then either (or both) selects the power path to be connected to the electronics package or severs the connections to the alternative paths. The present invention provides the solution to these needs.
The invention provides systems and methods for connecting an electronics package to an electrical path, while maintaining and fixing appropriate electrical isolation from other electrical paths. Among the many uses of the invention, the automatic power source selector is advantageously used in reversible circuit breakers having electronic fault detection components that require a connection to a power source. A circuit breaker that includes the invention may be installed in a plurality of orientations and will automatically connect the fault detection electronics to the appropriate power supply path.
The present invention comprises a system for selecting a power path from among a plurality of available power paths, connecting power paths and disconnecting unselected power paths, as required. A power source selection circuit is included in a reversible circuit breaker. The power source selection circuit detects the presence of a voltage on a one side of the reversible circuit breaker and disables the power path from a second side of the reversible circuit breaker to an electronics package included in the reversible circuit.
An inexpensive analog embodiment of the power source selection circuit is provided. The inexpensive analog embodiment uses power available on a first path to automatically detect and permanently interrupt a second power path. Power available from both power paths is used to remove the power source selection circuit from their connection to the power paths after the second power path is permanently interrupted.
The invention also provides a method to select a power path from a plurality of power paths and to automatically connect a selected path and/or disconnect an unselected path from an electronics package. The method tests the available power paths for a desired potential and then electrically isolates some or all of the remaining power paths. A method for installing a reversible circuit breaker that includes the present invention is also provided.